Stir together broth, soy sauce, cornstarch, and A 1/2 teaspoon salt until cornstarch ha dissolved.,Heat wok over high heat until a drop of water evaporates instantly.,Pour peanut oil down side of woke, then swirl oil, tilting wok to coat side.,______,Add half of bok choy and stir-fry until leaves wilt, about 2 minutes, then add remaining bok choy and stir-fry until all leave are bright green and limp, 2 to 3 minutes total.,Stir broth mixture, then pour into woke and stir-fry 15 seconds.,Cover with lid and cook, stirring occasionally, until vegetables are crisp-tender, 2 to 4 minutes.,Stir in sesame oil, then transfer to a serving dish.